1. Field of the Invention
The invention is concerned with thermal viewers.
High resolution thermal viewers are now state of the art. They generally operate in the wavelength region of one micron to fourteen microns. The images they produce are directly proportional in intensity to the temperatures of the objects or scenes under surveillance. The images, while quite different from visible images due to reflected light from the objects, are usually readily identified by the human observer. These images are thus described as signatures of the objects. In todays sophistocated computer systems these signatures are memorized and catalogued so that even subtle differences that escape human observation are available for identification of a specific target. In many ways the thermal image is a much more characterstic signature of the object than its visible image. This is because the image is emitted rather than reflected. It depends on the materials of which the object or target is made and the amount of material present. It often depends on the state of operation, as when the object contains a power source such as an internal combustion engine. Most important, however, is the inevitable effect of changes in the ambient temperature around the object. The chief causes of these changes are diurnal cycles of sunlight and air current or winds. There is usually a considerable disparity between the charges that occur in the object and those that occur in the background. At one time of day the object may almost blend into the background while at other times it will stand out in bold contrast.
2. Description of the Prior Art
It has, therefore, been the practice to study an object of interest by recording its images at various times of the day, in various types of backgrounds, at various times of the year and under various types of weather conditions. For many objects, e.g. tanks and large planes, this becomes very expensive and even tactically impossible. It also is virtually impossible where hostile objects are involved, even though a great deal of basic structural information on the object may be available.